This invention was made with Government support under Government Contract No. N00014-96-C-0145 awarded by DARPA. The Government may have certain rights to the invention.
This invention is related to the field of biofouling release coatings for use in industrial, commercial or military marine and freshwater applications. In particular, this invention relates to a method for regenerating a biofouling release coating which has decreased release efficacy due to depletion or lack of an incorporated oil.
Damage to underwater power cables, ships, and the like due to colonization of their surfaces by organisms (including, but not limited to, barnacles) has serious economic consequences in marine and freshwater industries. Antifouling and fouling release coatings have been developed to prevent or reduce biofouling, and to loosen the strength of the attachment of marine organisms to make cleaning surfaces easier. There are many commercial foul release coatings including, for example, GE EXSIL.RTM. 2200. However there have been no reports of renewal methods for these coatings.
There has been a continuing need in the coatings industry for new methods for increasing the useful life of fouling release and antifouling coatings. At present, the useful lifetime of a copper ablative antifouling coating is approximately three years, after which time the coating must be removed from the hull and reapplied. It is estimated that the effective life span of silicone fouling release coatings is about 5-7 years.
The release characteristics of silicone fouling release coatings are known to be significantly enhanced by the addition of oils such as mineral oil and silicone oils. Barnacle adhesion measurements on fouling release coatings substantiate that removal of fouling requires less work when the silicone topcoat has been prepared with incorporated oils. For example, silicone oils such as dimethyl silicone oils, phenyl-modified silicone oils, and polyether-modified silicone oils have been incorporated into biofouling release coatings.
Unfortunately, these additives tend to diffuse out of the coating during use and are thus rapidly depleted. The depleted coatings lose their enhanced foul-release properties, and consequently their effectiveness is reduced. Depletion of the additive therefore limits the useful life of the coating, necessitating periodic removal and reapplication of a new silicone biofouling release coating. A recoat technology for these coatings which does not require complete removal and reapplication of the coating would significantly reduce life- cycle costs and enhance the attractiveness of these coatings to the power utility, military, industrial, and commercial markets.
To forestall the rapid oil-depletion of oil-containing biofouling release coatings, larger amounts of oil have been incorporated into these coatings. This solution to the problem does curtail the rapid depletion of the oil, but unfortunately it tends to severely impair the mechanical properties of the coatings, particularly tear strength and abrasion resistance. Increasing the original additive content of biofouling release coatings, therefore, does not provide a workable method of increasing the life of the coatings.
Silicone biofouling release coatings made without additives also have been used to make cleaning surfaces of organisms easier, but they are not as effective as coatings with incorporated oils. A method for enhancing the properties of these coatings, as well as restoring the enhanced release properties of older coatings originally containing additives is highly desirable.